In database systems, data is often stored in tables as numerical data entries expressed in a particular unit. For instance, a vendor's database might maintain a table listing sales transactions that include the quantity of an item that was sold and the amount of money the item or items were sold for, expressed in some currency. From time to time, the vendor might want to convert the currency in which the sold items are expressed and might also want to perform other database operations on the table. Since the conversion of table entries as expressed in one kind of units to table entries expressed as another kind of units can be time and resource intensive, it can sometimes be desirable to minimize the number of table entries that must be converted.
In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.